In vivo and in vitro complex formation of prostate specific antigen with alpha 1-anti-chymotrypsin

Prostate-specific antigen-retargeted recombinant newcastle disease virus for prostate cancer virotherapy

Oncolytic virus (OV) therapies of cancer are based on the use of replication-competent, tumor-selective viruses with limited toxicity. Newcastle disease virus (NDV), an avian paramyxovirus, is a promising OV and is inherently tumor selective and cytotoxic only to tumor cells. Replication is restricted in normal cells. Despite encouraging phase I/II clinical trials with NDV, further refinements for tumor-specific targeting are needed to enhance its therapeutic index. Systemically delivered NDV fails to reach solid tumors in therapeutic concentrations and also spreads poorly within the tumors due to barriers including complement, innate immunity, and the extracellular matrix. Overcoming these hurdles is paramount to realizing the exceptional oncolytic efficacy of NDV. We engineered the F protein of NDV and generated a recombinant NDV (rNDV) whose F protein is cleavable exclusively by prostate-specific antigen (PSA). The rNDV replicated efficiently and specifically in prostate cancer (CaP) cells and 3-dimensional prostaspheres but failed to replicate in the absence of PSA. Induction of intracellular PSA production by a synthetic androgen analog (R1881) enhanced fusogenicity in androgen-responsive CaP cells. Further, PSA-cleavable rNDV caused specific lysis of androgen-independent and androgen-responsive/nonresponsive CaP cells and prostaspheres, with a half-maximal effective concentration (EC50) ranging from a multiplicity of infection of 0.01 to 0.1. PSA-retargeted NDV efficiently lysed prostasphere tumor mimics, suggesting efficacy in vivo. Also, PSA-cleavable NDV failed to replicate in chicken embryos, indicating no pathogenicity for chickens. Prostate-specific antigen targeting is likely to enhance the therapeutic index of rNDV owing to tumor-restricted replication and enhanced fusogenicity.

Distribution and secretory pathways of prostate specific antigen, alpha1-antichymotrypsin and prostate secretory granules in prostate cancers

Using 19 radical prostatectomy specimens, we studied the histological distribution of free prostate specific antigen (PSA), total PSA, alpha1-antichymotrypsin (ACT) and prostate secretory granules (PSG) in both normal and cancerous cells of the prostate. After glutaraldehyde fixation, numerous fine eosinophilic droplets of PSG could be found mainly in the apical portions of normal acinous epithelial cells, but was markedly decreased in cancer cells. With antibodies against free PSA, normal acinous cells were granularly positive in the apical portion of the epithelium, which corresponded to the PSG, whereas cancer cells were diffusely positive. With antibodies against ACT, normal duct cells and cancer cells were often positive, but few normal acinous cells were positive. Presumably, these findings indicate that free PSA is secreted into the lumen as PSG in normal glands, but not by the same pathway in cancers where free PSA appears to accumulate due to a decrease of PSG, then leak into the blood producing complexed PSA to some extent in the cytoplasm. One factor analysis of variance (ANOVA) on the correlation of tumor differentiation or Gleason score with serum values of total PSA, free PSA and a free/total PSA ratio demonstrated no significant links. Elucidation of secretory mechanisms should provide better comprehension of various PSA indices for prostate cancer screening.

Biochemical staging of prostate cancer

PSA continues to be one of the most effective and widely used cancer screening tools available. Its popularity in prostate cancer screening, however, has eroded its usefulness in the staging of this disease. As more men are screened every year on a routine basis with DRE and PSA, the average PSA at diagnosis has drifted down to well below 10 ng/mL in many centers, including ours. This trend is likely to accelerate, as a PSA cut off for prompting biopsy of the prostate of 2.5 ng/mL gains more widespread acceptance. The recent realization that, at these levels, serum PSA is more reflective of the presence of BPH than of the extent of cancer and, therefore, does not provide additional staging information, has renewed the search for new biochemical markers that are capable of predicting prostate cancer stage and prognosis. Because of the heterogeneity of this disease, it is unlikely that a single biochemical marker that is capable of accurately staging all prostate cancer patients will be found. For this reason, nomograms that are capable of integrating various parameters to predict stage and prognosis will remain indispensable. As new biochemical markers that provide independent predictive information about stage or prognosis are identified, they can be incorporated into currently available nomograms. Of the biochemical markers discussed in this article, IL-6sR and TGF-beta1 are the most promising. By incorporating them into a preoperative nomogram designed to predict PSA recurrence, we found that they improved the ability to predict biochemical recurrence by a statistically and clinically significant margin. The ability to stage prostate cancer and predict response to therapy has improved dramatically over the last 3 decades. Nevertheless, there is still a need for new biochemical markers that will improve the ability to predict an individual patient's stage and response to therapy. Incorporating these new markers into nomograms will enhance the ability to provide optimal care for each prostate cancer patient.

The impact of intraoperative manipulation of the prostate on total and free prostate-specific antigen

OBJECTIVES

It is well documented that mechanical manipulation of the prostate can elevate total PSA (t-PSA) levels in serum. However, less is known about its effects on free PSA (f-PSA) and the free-to-total PSA ratio (f/t-PSA). We therefore examined the impact of prostate manipulation on t-PSA and f-PSA during surgical procedures involving the prostate.

METHODS

Intraoperative blood samples for t-PSA and f-PSA measurement (Hybritech) were collected every 15 min during 14 radical retropubic prostatectomies (RRP) and 10 radical cystoprostatectomies (RCP).

RESULTS

Prostatic manipulation induced significant elevations in t-PSA and f-PSA during RRP and RCP. Postmanipulatory peaks were markedly higher for f-PSA than for t-PSA. The mean maximum f-PSA levels showed a 4.3- (RRP) and 7.9-fold (RCP) increase, followed by a rapid decline after prostate removal. t-PSA increased 1.2- (RRP) and 1.3-fold (RCP), and declined more slowly. Postmanipulatory f/t-PSA ratios also increased significantly, reaching mean elevations of +0.29 and +0.28 over preoperative ratios during RRP and RCP, respectively.

CONCLUSIONS

Prostate manipulation can induce transient increases in t-PSA, f-PSA and f/t-PSA in benign and malignant prostates. The extent of these alterations and their course over time must be taken into account when postmanipulatory changes in PSA forms are investigated. Timing of postmanipulatory venipunctures and the molar response ratio of t-PSA assays used (equimolar versus nonequimolar) seem to have substantial impact on the results of such studies.

Early management of prostate cancer: how to respond to an elevated PSA?

Support for prostate cancer screening efforts is provided by observational studies reporting decreases in prostate cancer-specific mortality in areas where screening is performed with digital rectal exam (DRE) and measurement of serum prostate-specific antigen (PSA) levels. The combination of PSA and DRE is an excellent cancer-screening tool with sensitivity and positive predictive value superior to that of mammography and breast exam. Use of percent free PSA further improves the specificity of PSA testing, particularly in the range of 4-10 ng/ml, at which most false positive PSA tests occur. Men older than 50 with a >10-year life expectancy should be considered for prostate cancer screening. Those with an abnormal DRE or a PSA above 4 ng/ml should be referred to a urologist for further discussion of the risks and benefits of a prostate biopsy. Furthermore, those with a significant change in either DRE or PSA results, or those at higher risk for prostate cancer with a PSA level above 2.5 ng/ml, should also be referred for evaluation.

Indicators of pathologic stage of prostate cancer and their use in clinical practice

Pathologic stage is the most reliable means of predicting the likelihood of curable prostate cancer at the time of definitive treatment. Its prediction is of the greatest importance to individuals with clinically localized disease, principally because of the therapeutic and prognostic implications. Multivariate models integrating variables that can be derived from clinical and pathologic assessment have been shown to be reliable and useful in urologic practice. Among these variables, the combination of clinical stage, serum PSA, and biopsy Gleason score provides reliable assessment of the risk for extraprostatic disease that can be used readily for counseling individual patients. Other biopsy-derived parameters may contribute additional information, but their value in multivariate analysis has not been validated in a multi-institutional setting. The development of new prognostic markers is a priority objective in current research to distinguish patients in whom cancer cannot be controlled by surgical treatment. For patients undergoing radical prostatectomy, definitive pathologic stage certainly will remain an important prognostic factor; therefore, clinical practice will continue to be determined by its accurate prediction.

Thiophilic interaction chromatography of prostate-specific antigen

Prostate-specific antigen (PSA) protein and complexes of PSA with alpha1-antichymotrypsin (PSA-ACT) or alpha2-macroglobulin (PSA-A2M) prepared in vitro, have strong affinity for different thiophilic gels (T-gel). Free PSA, and these PSA complexes can be isolated due to their affinity for T-gels. The average recovery of PSA from several of the T-gels, based upon ELISA measurements, was 84 to 94%. The data suggest that T-gel affinity can be explored for the purification of free and complexed PSA from various biologic fluids.

Diagnosis of localized prostate cancer: 10 years of progress

Advances in the diagnosis of early stage disease, and particularly the introduction of prostate-specific antigen (PSA) testing, have had a dramatic effect on the presentation and clinical management of prostate cancer during the past ten years. As a result, there have been significant epidemiological changes in countries where early diagnosis is recommended. The importance of PSA testing for the diagnosis of localized prostate cancer has become well established in clinical practice and this is reflected by improved outcomes from definitive treatment. The contribution of PSA-related parameters and molecular forms of PSA both to cancer detection and prediction of pathological stage continue to be explored. Concerns about the reliability of the standard sextant biopsy technique for cancer detection relate to the need for re-biopsy in a growing number of patients with negative biopsies and an increasing proportion of patients with low volume, multifocal disease. In men with cancer, additional prognostic information can be derived from biopsy findings, with important therapeutic implications. This relates also to the need for reliable markers indicating pathological stage and risk of progression. The opportunities for the prevention of prostate cancer have grown with improved understanding of its biology and the genetic basis of the early steps associated with malignant transformation. In the future, the need for therapeutic intervention is likely to be most influenced by successful prevention strategies.

Effect of prostatic biopsy on free-to-total prostate-specific antigen ratio in patients with prostate cancer

BACKGROUND

We determined the effect of prostatic biopsy on the changes in total and free prostate-specific antigen (PSA) and free-to-total PSA ratio (F/T ratio) and examined if there are differences in these parameters between patients with benign and malignant histologic findings.

METHODS

The concentration of total and free PSA and the F/T ratio were determined in 35 men before and 1 h after prostatic biopsy. The level of PSA was measured with a chemiluminescent enzyme assay. Of 35 patients, nine were diagnosed as having prostate cancer.

RESULTS

In patients whose biopsy revealed cancer, the F/T ratio was lower than those without cancer, although there were no differences in total and free PSA value before prostatic biopsy. One hour after prostatic biopsy, there was an increase in the level of total and free PSA and the F/T ratio in all men. The increase in the F/T ratio was greater in patients whose biopsies revealed no prostate cancer. In patients with stage B cancer, these parameters increased more than those with stage C/D cancer.

CONCLUSION

Prostatic biopsy causes a dramatic increase in total and free PSA. The F/T ratio also increased after biopsy. The PSA response to prostatic biopsy might be different in patients with and without prostatic malignancy. The response might also be different according to stage of prostate cancer.

Prostate specific antigen: a decade of discovery--what we have learned and where we are going

PURPOSE

Many advances have occurred during the last decade in the clinical use of prostate specific antigen (PSA) for detecting, staging and monitoring prostate cancer. We review the clinical usefulness and limitations of serum PSA as a tumor marker of prostate cancer.

MATERIALS AND METHODS

The English language literature was reviewed with respect to the major contributions and limitations of PSA in present clinical practice.

RESULTS

Although controversial, age specific PSA reference ranges can improve the sensitivity for prostate cancer detection in young men and the specificity in older men. Percent free PSA improves the specificity for prostate cancer detection in men with PSA values between 4 and 10 ng./ml., and a PSA density of greater than 0.15 may better distinguish benign prostatic hyperplasia from prostate cancer. PSA velocity can improve the ability to detect prostate cancer when 3 serial PSA values are measured during a 2-year period. For prostate cancer staging PSA is most useful combined with clinical stage and Gleason score in multivariate analysis. Percent free PSA may prove useful for staging prostate cancer but further clinical trials are needed to determine its clinical usefulness. PSA is the most clinically useful means to monitor disease recurrence after treatment of prostate cancer. With ultrasensitive PSA assays it is now possible to increase the lead time for detection of disease recurrence by several months.

CONCLUSIONS

During the last decade much of the focus has been on improving the ability of this tumor marker to detect prostate cancer. PSA remains the best and most widely used tumor marker in urology today.

Determination of alpha1-antichymotrypsin-PSA complex in serum does not improve the differentiation between benign prostatic hyperplasia and prostate cancer compared with total PSA and percent free PSA

OBJECTIVES

To evaluate the analytical performance and diagnostic utility of alpha1-antichymotrypsin (ACT)-prostate-specific antigen (PSA) complex in serum to improve the differentiation between benign prostatic hyperplasia (BPH) and prostate cancer (PCa).

METHODS

Serum concentrations of total PSA (tPSA), free PSA (fPSA), and ACT-PSA were measured in 112 untreated patients with PCa (median age 65 years), 34 patients with BPH (median age 66 years) with histologic confirmation, and 33 men without prostate disease and with a normal digital rectal examination considered as controls (median age 54 years). Sera were frozen at -80 degrees C within 2 hours after collection and then analyzed during a 12-week period. Determinations were made with the Enzymun-Test for tPSA and fPSA and with a prototype assay for ACT-PSA on the ES system (Roche Diagnostics, Boehringer Mannheim).

RESULTS

The new ACT-PSA assay showed reliable data of analytical performance. The lower detection limit amounted to 0.068 microg/L. The assay was linear to 50 microg/L. Spiking experiments showed a mean recovery rate of 98.2%. No interferences of the assay were observed in patients with acute inflammation and highly increased ACT concentrations. The values of intra- and interassay imprecision ranged from 1.51% to 3.48% and 2.1% to 6.3%, respectively. The median value of ACT-PSA concentrations were significantly different (P <0.001) between controls and patients with BPH and PCa (0.40, 3.86, 5.26 microg/L, respectively). The median fPSA/tPSA and fPSA/ACT-PSA ratios were significantly different between BPH and PCa (24.3% versus 12.2%, P <0.001 and 32.9% versus 15.0%, P <0.001, respectively), but no difference of the ACT-PSA/tPSA ratio was observed (78.2% versus 78.7%, P = 0.696). Receiver operating characteristics of ACT-PSA (area under the curve = 0.630) and all the derivative ratios of fPSA/ACT-PSA (area = 0.737) and ACT-PSA/tPSA (area = 0.528) were not different from that of tPSA (area = 0.619), but showed a lower discrimination power between BPH and PCa than the fPSA/tPSA ratio (area = 0.790).

CONCLUSIONS

Using this prototype assay to quantify ACT-PSA in serum, we have demonstrated that ACT-PSA and the calculated derivatives are not superior in the differentiation between BPH and PCa compared with tPSA and the ratio of fPSA to tPSA.

Two-dimensional electrophoresis of prostate-specific antigen in sera of men with prostate cancer or benign prostate hyperplasia

Prostate-specific antigen (PSA), the main marker for prostate cancer (PCa), is released from the prostate into the blood stream at nanogram level and may increase in PCa and nonmalignant disease such as benign prostate hyperplasia (BPH). More recently, advantage was taken of PSA's ability to bind to protease inhibitors in serum in order to improve discrimination between PCa and BPH, using the free PSA to total PSA ratio. The understanding of this phenomenon at molecular level, which is still unknown, may promise new improvements in the field of diagnostics. For this purpose, we determined the pattern of PSA forms in PCa and BPH sera, using the high resolving power of two-dimensional electrophoresis (2-DE) in conjunction with the high sensitivity of chemiluminescence detection. Serum PSA differs drastically from seminal PSA: apart from complexed forms, serum PSA shows few cleaved forms. Moreover, 2-DE patterns from PCa are relatively homogeneous, whereas patterns from BPH may in some cases present a higher proportion of cleaved forms and in other cases present slightly more basic spots. We therefore demonstrated, for the first time, that an increase in the free to total PSA ratio in BPH cases may be due to cleaved PSA forms (which are enzymatically inactive and unable to bind inhibitors), or possibly related to basic free PSA, which may represent the zymogen forms.

Human Kallikrein 2 (hK2) and prostate-specific antigen (PSA): two closely related, but distinct, kallikreins in the prostate

Recent studies on human kallikrein 2 (hK2) have revealed striking similarities and significant differences with the closely related kallikrein PSA. Both PSA and hK2 are primarily localized to the prostate and share close structural similarities. Although both kallikreins are produced by the same secretory epithelial cells in the prostate, hK2 is associated more with prostate tumors than PSA and is highly expressed in poorly differentiated cancer cells. The potent trypsin-like activity of hK2 contrasts with the weak chymotrypsin-like activity of PSA. The inactive precursor form of PSA, proPSA, is converted rapidly to active PSA by hK2, suggesting an important in vivo regulatory function by hK2 on PSA activity. The high homology between hK2 and PSA results in significant cross-reactivity to hK2 by polyclonal and some monoclonal antibodies to PSA. Future studies on both PSA and hK2 need to take into account this potential for cross-reactivity. Specific monoclonal antibodies to hK2 have now demonstrated that serum levels of hK2, like PSA, are correlated with prostate cancer. The production of hK2 protein in active protease form and specific monoclonal antibodies to the hK2 antigen will allow extensive future studies delineating the physiological and clinical utility of this new prostate antigen.

Prostate-specific antigen in the cerebrospinal fluid leads to diagnosis of solitary cauda equina metastasis: a unique case report and review of the literature

A 79-year-old male patient presented with a subacute cauda syndrome caused by an intradural metastasis of the lumbosacral caudate fibres from an adenocarcinoma of the prostate, which had been treated 5 years earlier with external beam radiation therapy. Diagnosis could not be established by repeated magnetic resonance images (MRIs) during a 2-year period of increasingly severe radicular pain. Eventually, a small tumour mass could be visualized on the fourth MRI. Repeated normal serum prostate-specific antigen (PSA) did not hint at a prostate cancer metastasis (range 2.4-5.1 ng ml(-1)); however, PSA in the cerebrospinal fluid was found to be elevated (29.1 ng ml(-1)). Empirical radiation therapy of the caudate region did not improve radicular pain. Therefore, an exploratory surgical procedure was conducted, which confirmed the suspicion of an intradural prostate cancer metastasis. In conclusion, PSA in the cerebrospinal fluid provides a useful diagnostic tool for detecting intradural prostate cancer metastasis.

Molecular forms of prostate-specific antigen and human kallikrein 2 (hK2) in urine are not clinically useful for early detection and staging of prostate cancer

OBJECTIVES

Prostate-specific antigen (PSA), a member of the human kallikrein (hK) family, is the most important tumor marker for early detection, staging, and monitoring of men with prostate cancer today. However, the sensitivity of serum PSA is not sufficient to be used alone for prostate cancer screening. Recently, it was reported that the serum-to-urinary total PSA ratio improves the detection of men with prostate cancer, especially in men with a serum total PSA level between 4.0 and 10.0 ng/mL. We tested this hypothesis by evaluating the clinical usefulness of this PSA ratio as well as the use of the different molecular forms of PSA and human kallikrein 2 (hK2) in urine for detection and staging of prostate cancer.

METHODS

One hundred ten fresh, midstream urine specimens (prostate cancer 62, benign prostatic hyperplasia [BPH] 38, healthy male control 5, women 5) were collected. Serum total PSA, urine total PSA, urinary free PSA, urinary alpha 1-antichymotrypsin-bound PSA, and urinary hK2 levels were determined by monoclonal antibody assays (Hybritech Inc.). The serum-to-urinary total PSA ratio was calculated.

RESULTS

The serum-to-urinary total PSA ratio did not accurately distinguish between men with BPH and men with prostate cancer. There was no significant difference between the urinary levels of any of the molecular forms of PSA or hK2 between men with prostate cancer and men with BPH. Among men with prostate cancer, neither urinary hK2 nor urinary levels of any of the molecular forms of PSA correlated with age, pathologic stage, or Gleason grade.

CONCLUSIONS

In our study, the serum-to-urinary total PSA ratio did not improve the detection of men with prostate cancer. Furthermore, measurement of the molecular forms of PSA and hK2 in urine did not improve the detection or staging of prostate cancer over serum PSA alone.

The use of prostate-specific antigen and free/total prostate-specific antigen in the diagnosis of localized prostate cancer

Although there is controversy regarding the benefit of early detection of prostate cancer, it has been demonstrated that early detection can be best achieved through the use of a combination of digital rectal examination and prostate-specific antigen (PSA). This article outlines the clinical use of PSA for early detection of prostate cancer and focuses primarily on the value of molecular forms of PSA (free PSA, complexed PSA, and total PSA) in the diagnosis of localized prostate cancer.

Serum free prostate specific antigen: isoenzymes in benign hyperplasia and cancer of the prostate

Prostate specific antigen (PSA) in serum of patients with benign prostatic hyperplasia (BPH) or prostate cancer (P-CA) not bound to alpha-1-antichymotrypsin (ACT) was analyzed by chromatofocusing. The procedure allowed the simultaneous separation of complexed and free PSA and the fractionation of the free PSA fraction into several isoenzymes. The detection of the isoenzymes was strongly dependent on the combination of antibodies introduced in the applied commercially available immunoassays (Cobas Core, Delfia). Isoenzymes in sera of patients with benign prostatic hyperplasia were mainly situated in the pI range of 6.6 to 7.3. Isoenzymes in sera of prostate cancer patients or in PSA from LNCAP cells were mainly situated in the pI range 7.0 to 8.3. Neuraminidase treatment of the sera shifted the isoelectric points of all three sources towards more basic pHs. An irregular glycosylation process in the dysplastic cells of the prostate is suggested to be the cause for the shift of the isoelectric points. The difference of isoenzyme distribution along the pH axis is discussed as a diagnostic tool to differentiate between BPH and P-CA.